Earlier research by Dr. William C. Rose (Nutr. Abst. Rev. 27, 631 (1957)) indicated that an oral source of histidine was not needed for the maintenance of nitrogen balance in young, adult human subjects. Later authors have questioned the conclusion that histidine was non-essential. Our reported experiment showed that an adult human was maintained for 48 days with all amino acids supplied by central intravenous alimenation (Wixom et al., Am. J. Clin. Nutr. 30, 887 (1977)). Within this experiment, the deletion of histidine for 27 days resulted in a continued close-to-zero corrected nitrogen balance. After ingestion of 15NH4Cl, the incorporation of 15N into the ring of histidine indicated limited synthesis of histidine (Sheng, Y-B. et al., J. Nutr. 107, 621 (1977)). An essential fatty acid deficiency was observed during the above lipid-free parenteral nutrition (1972-3, experiment) in both man and the miniature Sinclair pig (Terry, B. E. et al., Am. J. Clin. Nutr. 30, 900 (1977); Badger, T.M. et al., J. Parenteral Enteral Nutr. 2, 116 (1978)). Many other measurements were described in these four papers, the review in press (Wixom, R. L. et al., 1979), and those of my colleague, Dr. Helen L. Anderson. Subsequent research has focused on the role of histidine in selected animals and clarification of the above interrelationships has continued by research with 15N and 14C studies. These findings and the results of others must be considered in the evaluation of histidine's role for normal man and specified animals.